General Review of GRAAL physics : Achievements and Future
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General Review of GRAAL physics :Achievements and Future
D. Rebreyend LPSC Grenoble
(GRAAL Collaboration)
MENU04, 30 August ’04
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Outline
GRAAL set-up Meson photoproduction on the proton Eta photoproduction on the neutron HYDILE polarized HD target
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Compton Beam
(nm) E(MeV)
514 1100
351 1483
300 1660
Energy Spectrum Polarisation
Simulation
Experiment
EeESRF = 6027.6 0.6
MeV
Linear
Circular
tag~ 10 6 /s
FWHM=16 MeV
Tagged
region
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LAGRANE Detector
1: Compton beam 2: Liquid H2/D2 target
3: BGO Calorimeter 4: Cylindrical MWPC’s
5: Plastic Barrel 6: Plastic Wall
7: Plane MWPC’s 8: Shower Wall
Shower Wall
• neutron efficiency 20 %
• / neutron PID
ToF
E
250
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GRAAL Domain
• E = .6-1.6 GeV/ W=1.4-2 GeV
• Region of second and third resonance
• , K, ’ thresholds
• Complementary of LEGS and LEPS
’ threshold
threshold
K threshold
LEGS/BNL LEPS/SPRING8
E (GeV)
(
b)
threshold
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Meson Photoproduction on the proton
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Survey of GRAAL Results Published
+n: from 700 to 1500 MeV (PLB ’00 and ’02) p : and d/d from threshold to 1100 MeV (PRL ’98, PLB ’02)
00p: and d/d from 700 to 1500 MeV (PRL ’03)
Close to completion 0p: and d/d from 700 to 1500 MeV p : extension to 1500 MeV
In progress p : comparison neutral (0 ) / charged decay (+0) K and K
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K AnalysisChannel selection
• 3 tracks in MWPC’s
• 2-body kinematical constraints calculation of 3 momenta
• PID by combining calculated momenta with E and/or ToF
important check: vertex reconstruction
p + - K
Distance (primary-secondary) vertices
(No efficiency correction)
Distance (primary-secondary) vertices
(No efficiency correction)
c = 7.6 cm
(PDG: 7.89 cm)
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Azi
muth
al dis
trib
uti
on
NH+NV NV-NH/NH+NV
P
Beam Asymmetry
Recoil Polarization (linear polar.)
Px = P Ox sin21 - Pcos2
Py = P - P T cos2/ 1 -
Pcos2
Pz = P Oz sin21 - Pcos2
1.2 GeV
1.4 GeV
1.05 GeV
1.2 GeV
1.4 GeV
1.05 GeV
angular distributionangular distribution
P angular distributionP angular distribution
Good agreement with LEPS
PRL ‘03
d/d = (d/d)0{1 – P cos(2) }
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Cross SectionC
ount
s/do
se (
a.u.
)C
ount
s/do
se (
a.u.
)
p K+ p K+
p K+ p K+
SAPHIR data (EPJ ’04)
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Eta photoproduction on the neutron
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• SAID analysis : Possible narrow N* at 1680 and/or 1730 MeV
• Polyakov & Rathke (EPJ A18 (03)) :Dominance of photoproduction on the neutron for N10
look for reactions : n N10 n, K0 , K+ -
Recent Motivation Soliton Model anti-decuplet
Non-exotic resonance with a narrow width 10 MeV
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Preliminary Remarks Grenoble analysis (A. Lleres) Studied channels :
d +
n K0 n K+ -
n n (“ easy channel ”) cross section Comparison p p proton target / deuteron target Preliminary results (error bars only statistical) No Fermi momentum correction:
width structure (E)100-130 MeV
No evidence but statistics is too poor for
definite conclusion
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n(p) n(p) Event Selection
• Identical geometrical acceptances for n and p
• Selection of “Quasi-Free kinematics” ??
All final state particles detected: 2 + n (p) proton/neutron detected at forward
angles : lab 250
2 detected in BGO : lab 250
Selection by invariant mass and
2-body kinematical angular correlations no recoil proton/neutron
n / p
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Invariant Mass
p : 0.6 % (taking p= n ) n : 0.3 %
N N : 1-3 %
1.2 % 0.9 %
n n n n p p p p
Simulation
Data
Small background
Background
estimates
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p p Differential Cross Section : Free/Quasi-free
d/
d
(b
/sr)
CM = 1620
Distributions at fixed CM (backward) angles versus E
CM = 1480
CM = 1390
CM = 1230 CM
= 1170
CM = 1300 CM
= 1100 CM = 1040
Clear Discrepancy below 1100 : Data Analysis / Physics ?
not quasi-free reaction close to 1000
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n n Differential Cross Section
• No prominent peak
• Structure at E 1.05 GeV (W 1.7GeV)
• Marked Angular Dependence
d/d (b/sr) at fixed CMd/d (b/sr) at fixed CM
CM = 1540 CM
= 1340
CM = 1200 CM
= 1070
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Comparison QF neutron vs QF proton (1)Ratio QF neutron/QF proton
R=dn/dp at fixed CMR=dn/dp at fixed CM
• Ratio 0.6-0.5 below 900 MeV
(Bonn, R=0.68 PRL ’97)
• Sudden rise around 1 GeV resonance
(Kouznetsov, Moscow seminar, April ’03)
CM = 1540 CM
= 1340
CM = 1200 CM
= 1070
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Comparison QF neutron vs QF proton (2)Integrated Cross Section (p,n 250)
• No “narrow” peak observed in neutron cross section but
shoulder for neutron above 900 MeV
• Rise in difference (neutron-proton) compatible with “narrow” structure
neutron
normalized QFproton
neutron
normalized QFproton*
neutron – C x protonneutron – C x proton
Simulated peak :
W=1.68 GeV, = 10 MeV
Because of Fermi motion :
FWHM = 127 MeV
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Comparison QF neutron/QF proton (3)Integrated ( n) Invariant Mass (p,n 250)
• No peak : compatible with behaviour of d/d
• Spreading due to Fermi motion Resolution
( n) Invariant Mass (GeV)
neutron
normalized proton
neutron
normalized proton*
neutron – C x protonneutron – C x proton
Simulated peak :
W=1.68 GeV, = 10 MeV
Because of resolution :
FWHM = 96 MeV
Num
ber
of e
vent
s
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Beam Asymmetry
See R. Di Salvo’s talk in Parallel Session for more details
n n n n p p p p
Bea
m A
sym
met
ry
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HYDILE target
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Operating Principle & Performances Pure HD
good dilution factor (15 % Al)
n and p are polarized
“Relaxation Magnetic Switch” principle (Hoenig ’67)
o-H2 impurities used to polarize (HD weakly coupled to lattice)
o-H2 decays to p-H2 in a few days HD spins decoupled from lattice
relaxation time / 1/ o-H2 concentration
Fabrication process
polarization of HD with static method in a Dilution Refrigerator (17 T, 10 mK)
at Orsay
aging process in DR for 2-3 months 1 T, 1 K
transport from Orsay to Grenoble
Expected performances
polarization : 80 % for p and 20 % for d (50 % with FAP)
relaxation time : 1-2 weeks
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Dilution Refrigerator (Orsay)
In-beam + transfert cryostats (Grenoble)
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First run with polarized HD in November 2004
Recent achievements
• Installation of Transfer (TC) and In-beam cryostats (IBC) in Grenoble (10/03)
• Running of IBC during 3 days at 1.5K (11/03)
• First complete and successful transfer of an unpolarized HD sample from Orsay to Grenoble (April 2004)
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Summary
p and K, : results will be released in a “near” future
n n : preliminary results on d/d have been obtained at neutron forward angles ( 250) No prominent peak but structure is observed around W=1.7 GeV
not seen on the proton Extension to all angles foreseen
First data with HYDILE target scheduled in November!!
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Proton Beam Asymmetry
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Neutron Beam Asymmetry
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K0 Analysis
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K0results
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European Synchrotron Radiation Facility
• Circumference : 844 m
• 40 beamlines
• Ee = 6.03 GeV
• Ie = 200 mA
• Bunch structure = 2.8 ns
ESRF parameters
GRENOBLE